In recent years, highly efficient motors have been demanded along with increasing energy saving consciousness, and there have been proposed a large number of interior permanent magnet motors using rare-earth magnets having high residual magnetic flux density and coercivity in a rotor to achieve high efficiency. Further, employment of structure in which the magnets are embedded in the rotor allows to use a reluctance torque as well as a magnet torque, thereby being available of constructing the highly efficient motor. The reluctance torque is proportional to a difference in inductance between a d-axis and a q-axis. Thus, in order to improve the reluctance torque, in general, it is desired to employ structure in which a q-axis magnetic flux easily passes therethrough and a d-axis magnetic flux less easily passes therethrough.
Meanwhile, in order to improve the magnet torque, it is desired to employ structure that can effectively use the magnetic flux of the magnet, and it is necessary to reduce a leakage magnetic flux. As a measure for reducing the leakage magnetic flux of the interior permanent magnet motor, it is effective that the thickness of each of thin portions between ends of a magnet insertion hole and a rotor surface is reduced to reduce a magnetic flux passing through each of the thin portions.
For example, in Patent Literature 1, there is disclosed structure in which the interval between the magnet insertion holes of the rotor is set larger than the tooth width of the stator, and the width of each of concave portions of the rotor outer surface at the vicinities of the ends of the magnet insertion hole is set larger than the interval between the above-mentioned magnet insertion holes, thereby being available of obtaining both the magnet torque and the reluctance torque.